Wikipedia
Libpolo
libpolo is a graphics, sound and network library written in C and is designed for educational environments. Libpolo is free and open-source software, subject to the requirements of the GNU General Public License (GPL) version 2 or any later.
It is aimed towards students learning the C and C++ programming languages, and it is very suitable for high school and first-year university courses.
Its functionality is built around the GLUT library. It provides a streamlined interface, also allowing full access to the OpenGL API.
It is cross-platform and works under Linux, Microsoft Windows and OS X.